Schistosome infections are studied quantitatively in man and in experimental animals. Experimental Schistosoma japonicum infections in rabbits produce severe hepatic fibrosis which shares some anatomic similarities with Symmers' clay pipestem fibrosis in man. Collagen synthesis and degredation in these livers are being examined in collaborative studies. Intestinal, but not hepatic, lesions have varied greatly with the strain of schistosome used to infect rabbits. In infected Egyptian patients examined at autopsy, cor pulmonale attributable to schistosome infection was always accompanied by schistosomal pulmonary arteritis and was seen only in cases with s. mansoni infection and Symmers' fibrosis.